Powder for achieving hemostasis

ABSTRACT

In various aspects, the present disclosure pertains to methods of treating or preventing bleeding at a tissue site comprising applying a chitosan powder composition to the tissue site. In various aspects, the present disclosure pertains to chitosan powder compositions for application to a tissue site, where the powder compositions comprise a chitosan salt, a crosslinked chitosan, a derivatized chitosan, or a combination thereof. In various aspects, the disclosure pertains to catheter assemblies, which are preloaded with a chitosan powder composition and which are configured to deliver the chitosan powder composition a tissue site.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/616,751, filed Jan. 12, 2018, entitled “Powder for Achieving Hemostasis,” the disclosure of which is hereby corporate by reference in its entirety.

BACKGROUND

Gastrointestinal bleeding affects millions of people annually. Certain cases of internal bleeding cannot be controlled effectively by current hemostatic technologies such as clips, cautery, or band ligation. Wounds, surgical sites, diseased tissue, ulcer beds and gastric varices, among others, are locations where conventional means of hemostasis may to fail, leading to extended hospital stay or death.

SUMMARY

In various aspects, the present disclosure pertains to methods of treating or preventing bleeding at a tissue site comprising applying a chitosan powder composition to the tissue site, wherein the chitosan powder composition comprises a chitosan salt, a crosslinked chitosan, a derivatized chitosan, or a combination thereof.

In various embodiments, the tissue site may be a body lumen, for example a site in the gastrointestinal tract. When the tissue site is a body lumen, the chitosan powder may be applied, for example, via a catheter or other suitable device.

In various embodiments, which may be used in conjunction with the above aspects and embodiments, the powder may be fluidized in a gas (e.g., CO₂, nitrogen, air, etc.) to form a fluidized powder and blown onto the tissue site. In such embodiments, the fluidized powder may exit the catheter at a velocity ranging from 1.5 to 50 m/s, among other possible velocities.

In various aspects, the present disclosure pertains to powder compositions for application to a tissue site, where the powder compositions comprise first particles comprising chitosan, a chitosan salt or a derivatized chitosan admixed with second particles that comprise a crosslinking agent that covalently or non-covalently interacts with the first particles upon exposure to moisture.

In some embodiments, the first particles may comprise a chitosan salt and the crosslinking agent may be a polyanionic crosslinking agent. For example, the first particles may comprise chitosan or a chitosan salt and the crosslinking agent may be a covalent crosslinking agent. Examples of covalent crosslinking agents include, for instance, a multifunctional epoxy, a multifunctional aldehyde, multifunctional acrylate, genipin, or a derivatized polymer (e.g., an aldehyde derivatized polymer, an epoxy derivatized polymer, acrylate derivatized polymer or a genipin derivatized polymer), among other possibilities.

In some embodiments, which may be used in conjunction with the above aspects and embodiments, the first particles may comprise a derivatized chitosan and the second particles may comprise a covalent crosslinking agent. In one particular example, the first particles may comprise thiol-modified chitosan and the second particles may comprise a molecule having a plurality of unsaturated groups.

In various aspects, the present disclosure pertains to powder compositions for application to a tissue site that comprise derivatized chitosan.

In some embodiments, the derivatized chitosan reacts with cysteine groups in tissue upon exposure to moisture. For example, the derivatized chitosan may be chitosan derivatized with a multifunctional aldehyde, the derivatized chitosan may be chitosan derivatized with a multifunctional epoxide, the derivatized chitosan may be chitosan derivatized with a multifunctional acrylate, or the derivatized chitosan may be chitosan derivatized with genipin.

In some embodiments, which may be used in conjunction with the above aspects and embodiments, the derivatized chitosan may interact with thiol groups in tissue upon exposure to moisture.

In some embodiments, which may be used in conjunction with the above aspects and embodiments, the derivatized chitosan may be chitosan derivatized with unsaturated groups or the derivatized chitosan may be derivatized with thiol groups, among other possibilities.

In various aspects, the present disclosure pertains to powder compositions for application to a tissue site that comprise a chitosan salt.

In some embodiments, the chitosan salt ionically crosslinks with negative charged species in tissue or blood.

In various aspects, which may be used in conjunction with the above aspects and embodiments, the disclosure pertains to catheter assemblies, which are preloaded with a chitosan powder composition and which are configured to deliver the chitosan powder composition a tissue site.

These and other aspects and embodiments are further described in the detailed description to follow.

DETAILED DESCRIPTION

In various aspects, the present disclosure pertains to methods of treating a tissue site (e.g., a wound, a surgical site, a diseased tissue site, an ulcer bed, a gastric varix, etc.), in which a chitosan powder is applied to the tissue site. The chitosan powder may be applied, for example, to address existing bleeding or to prevent or minimize future bleeding that may occur. In various embodiments, the tissue site is tissue that surrounds a body lumen, for example, a wall of the gastrointestinal tract. The chitosan powder may contain, for example, chitosan, a chitosan salt, crosslinked chitosan, derivatized chitosan, or natural or synthetic polymer blends containing the same. As discussed in more detail below, in particular embodiments, the chitosan powder may comprise, for example, a chitosan salt, a crosslinked chitosan a derivatized chitosan or a combination thereof.

In various embodiments, the chitosan powder may be applied to a tissue site via a catheter. Examples include catheter assemblies in which a powder may be fluidized in a gas (e.g., compressed air, nitrogen, carbon dioxide, etc.) to form fluidized powder, which is then blown onto the tissue site. For example, a catheter assembly may be provided, which includes (a) a catheter having a lumen extending therethrough, a proximal end, and a distal end having an exit orifice, and (b) a reservoir containing a chitosan powder. The catheter assembly may be configured to deliver the chitosan powder from the reservoir, through the lumen, and out the exit orifice. In certain embodiments, the catheter assembly may include a pressurized reservoir that contains a pressurized gas for delivering the chitosan powder from the reservoir, through the lumen, and out the exit orifice. For example, the pressurized reservoir may be positioned upstream of the reservoir and the pressurized gas passed through the chitosan powder, thereby fluidizing the chitosan powder in the gas for delivery of through the lumen and out the exit orifice. In certain embodiments, the catheter is operated such that the fluidized powder exits the catheter at a velocity ranging from 15 m/s to 50 m/s. Where applied to the gastrointestinal tract, the chitosan powder may be applied through an endoscope.

In various aspects, the present disclosure pertains to catheters that are preloaded with a chitosan powder. For example, a system may be provided, which includes a catheter having a proximal end and a distal end that is partially loaded with chitosan powder (with a remaining volume being air). The catheter may also include a seal, such as a plug, cap, or other mechanism for retaining the chitosan powder on the proximal and distal ends of the catheter. The system may further be provided with a mechanism for breaking the proximal seal and for applying gas to the catheter at sufficient pressure to fluidize the powder in the catheter, eject the distal seal, and disperse the fluidized chitosan powder from the distal end of the catheter and onto the treatment site.

When applied to a tissue site, chitosan powder in accordance with the present disclosure acts as a barrier to bleeding associated with the tissue site. The chitosan powder acts as a barrier by absorbing liquids, which, for example, may be bodily fluids such as blood or gastrointestinal fluids (e.g., pancreatic juices, biliary fluid, saliva, etc.) that are present at the tissue site, or may be fluid such as saline, phosphate buffered saline, or contrast fluid that is applied to the tissue site prior to, concurrently with, or subsequent to application of the chitosan powder. The chitosan powder may be used to achieve hemostasis at sites of active bleeding or can be used as a preventative over clipped areas, suture sites, or other having the potential for bleeding, among other uses.

In various aspects, the present disclosure pertains to chitosan powders, that may be used to for hemostasis, among other possible uses.

Chitosan powders for use in the present disclosure may be of any suitable particle size. In various embodiments, the particle size may range, for example, from less than 1 μm to 1000 μm (e.g., ranging from 1 μm to 2.5 μm to 5 μm to 10 μm to 25 μm to 50 μm to 100 μm to 250 μm to 500 μm to 1000 μm), among other possibilities. In this regard, a chitosan powder having particles sized between 50 μm and 425 μm performs well when dispensed through an 8 French catheter.

As noted above, chitosan powder may contain, for example, chitosan, a chitosan salt, derivatized chitosan, or crosslinked chitosan, and, optionally, a natural or synthetic polymer.

Chitosan is a modified polysaccharide containing randomly distributed β-(1-4)-linked D-glucosamine and N-acetyl-D-glucosamine monomer units. Chitosan is produced commercially by the alkaline N-deacetylation of chitin, which is a cellulose-like polymer consisting primarily of unbranched chains of modified glucose, specifically N-acetyl-D-glucosamine.

The degree of deacetylation in commercial chitosans typically ranges from 75 to 100% although essentially any degree of deacetylation is possible. Chitosan is positively charged in acidic to neutral solutions with a charge density that is dependent on the pH and the degree of deacetylation. The pka value of chitosan generally ranges from 6.1 to 7.0, depending on the degree of deacetylation. Thus, while typically substantially insoluble in distilled water, chitosan is generally soluble in aqueous acidic solutions (e.g., pH ^(˜)6.5 or less).

Examples of chitosan salts include chitosan halides such as chitosan fluoride, chitosan chloride, chitosan bromide, chitosan iodide, chitosan phosphate, chitosan nitrate, chitosan sulfate, chitosan salts of organic mono-acids such as formate, acetate, propionate, butyrate, chitosan salts of organic diacids such as oxalate, malonate, succinate, maleate, or glutarate, or salts of hydroxyacids such as glycolate, lactate, tartrate, malate, citrate, or gluconate.

In various embodiments, modified chitosans may be employed, which exhibit enhanced properties, including enhanced adhesion. For instance, a thiol-modified chitosan may be formed by reaction of chitosan with a molecule having one or more thiol groups and one or more additional groups (e.g., carboxylic acid groups, which may also be referred to herein as carboxyl groups) for bonding to the chitosan. In a specific example, carboxylic acid groups of thiolactic acid may be reacted with primary amine groups on the chitosan through suitable chemistry to form a covalent amide bond. For example, carbodiimide conjugation works by activating carboxylic acid groups with a suitable carbodiimide, such as 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), dicyclohexylcarbodiimide (DCC), N,N′-diisopropylcarbodiimide (DIC), for direct conjugation to primary amines (e.g., primary amine groups on the chitosan) via amide bond formation. Similarly, carbonyldiimidazole (CDI) can be used in non-aqueous conditions to activate carboxylic acids for direct conjugation to primary amines (e.g., primary amine groups on the chitosan) via amide bonds. The thiols on the modified chitosan can provide enhanced attachment by interacting and forming covalent bonds with cysteine-rich tissue.

Other examples of modified chitosans include chitosan modified with groups that allow for covalent reaction with tissue, including groups that are reactive with amine groups found in tissue. For example, a multifunctional (e.g., difunctional, trifunctional, etc.) reactive molecule such as a multifunctional aldehyde molecule can be reacted with amine groups on chitosan to form aldehyde-modified chitosan (chitosan having pendant aldehyde groups). As another example, a multifunctional (e.g., difunctional, trifunctional, etc.) reactive molecule, such as a multifunctional epoxide molecule, can be reacted with amine groups on chitosan to form epoxy-modified chitosan (i.e., chitosan having pendant epoxide groups). As another example, a multifunctional (e.g., difunctional, trifunctional, etc.) reactive molecule, such as a multifunctional acrylate molecule or another molecule having one or more groups that react with chitosan and has at least one acrylate group such as PEG diacrylate, can be reacted with thiol groups on thiol modified chitosan via michael addition click reaction under body temperature in physiological pH conditions to form a chitosan-PEG crosslinked network (i.e., chitosan-PEG crosslinked gel having excess pendant thiol groups amendable to covalently linking to tissue). As another example, a multifunctional (e.g., difunctional, trifunctional, etc.) reactive molecule, such as genipin, can be reacted with amine groups on chitosan to form genipin-modified chitosan (i.e., chitosan having pendant genipin groups). In certain specific embodiments, the multifunctional reactive molecule (e.g., multifunctional aldehyde molecule, a multifunctional epoxide molecule, or genipin) may be reacted with chitosan in relative amounts such that multifunctional reactive molecule is provided in a 1×molar minimum relative to the number of moles of amine groups on the chitosan, such that all or essentially all of the amine groups are reacted and have pendant reactive groups.

Example of multifunctional aldehydes include glutaraldehyde, glyoxal, and aldehyde terminated hydrophilic polymers. Example of multifunctional epoxides include 4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, and epoxide terminated hydrophilic polymers. Hydrophilic polymers which may be provided with aldehyde or epoxide termination include poly(ethylene glycol) (PEG), also referred to as poly(ethylene oxide) (PEO), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), polyacrylamide, poly(acrylic acid), and poly(hydroxyethyl methacrylate) (PHEMA), Suitable hydrophilic polymers may range, for example, from 2 to 250 monomers in length, among other possibilities.

In certain specific embodiments, a modified chitosan may be formed by reacting a reactive synthetic molecule such as PEG diepoxide or a PEG dialdehyde with chitosan in relative amounts such that the reactive molecule is provided in a 1×molar minimum relative to the number of moles of amine groups on the chitosan, such that all or essentially all of the amine groups of the chitosan are reacted and have pendant epoxide-terminated PEG groups or aldehyde-terminated PEG groups.

In some embodiments, the chitosan may be directly oxidized, thereby forming aldehyde groups on the chitosan.

In some embodiments, a chitosan powder may be employed in which chitosan, chitosan salt, modified chitosan, or a combination thereof, is non-covalently crosslinked or covalently crosslinked, either before application to a tissue site, or at the time of application to a tissue site.

For instance, in some embodiments, an ionic crosslinker such as a multifunctional anionic molecule having two or more anionic groups (e.g., carboxylic acid groups, or sulfonate groups) may be provided in order to ionically crosslink the chitosan via positively charged amine groups located on the chitosan, Examples of multifunctional anionic molecules include organic diacids such as oxalate, malonate, succinate, maleate, or glutarate, or salts of hydroxyacids such as tartrate, malate, or citrate. Examples of multifunctional anionic molecules also include polyanionic polymers.

In some embodiments, the multifunctional anionic molecule is combined and ionically crosslinked with the chitosan prior to applying to tissue, grinding the crosslinked product into a powder if desired or necessary. In some embodiments, the multifunctional anionic molecule is ionically crosslinked on the tissue surface. For example, a multifunctional anionic molecule (e.g., citric acid, among others) may be combined with chitosan in powder form and the mixture applied to tissue. When this mixture contacts a moisture rich environment (e.g., provided by body fluid and/or a separately applied fluid), liquid will be absorbed and the powder constituents will dissolve and crosslink, creating a firmer more cohesive gel with less particulate over the application site.

In some embodiments, chitosan or modified chitosan may be covalently crosslinked prior to administration, and subsequently applied to tissue. For instance, chitosan or modified chitosan may be reacted with a multifunctional molecule having two or more groups (e.g., carboxylic acid groups, amine groups, epoxy groups, or aldehyde groups) that are reactive with the chitosan (e.g., reactive with the amine groups on the chitosan or carboxymethyl groups on the modified chitosan). For example, a biocompatible hydrophilic polymer (e.g., one the hydrophilic polymers listed above, among others) having terminal carboxylic acid groups may be reacted with primary amine groups on the chitosan through any suitable chemistry (e.g., using carbodiimide or carbonyldiimidazole chemistry) in order to covalently crosslink the chitosan. In one specific embodiment, carboxylic acid groups of a PEG dicarboxylate may be reacted with amine groups of chitosan using carbodiimide or carbonyldiimidazole chemistry, thereby covalently crosslinking the chitosan. As another example, a derivatized chitosan (e.g., a chitosan derivatized with carboxylic acid groups) is crosslinked with a biocompatible hydrophilic polymer (e.g., one the hydrophilic polymers listed above, among others) having terminal amine groups through any suitable chemistry (e.g., using carbodiimide or carbonyldiimidazole chemistry) in order to covalently crosslink the chitosan. In one specific embodiment, amine groups of a PEG diamine may be reacted with carboxylic acid groups of carboxymethyl chitosan using carbodiimide or carbonyldiimidazole chemistry, thereby covalently crosslinking the chitosan. The resulting product is subsequently applied to tissue, after grinding the product into a powder, if desired or necessary. This should generally improve the overall structural integrity of the powder.

In some embodiments, a chitosan powder is provided, which become covalently crosslinked upon administration to tissue.

For example, a first powder comprising a multifunctional (e.g., difunctional, trifunctional, etc.) reactive molecule that reacts with amines, for example, genipin, a multifunctional aldehyde molecule, or a multifunctional epoxide molecule, such as those described above (e.g., PEG diepoxide, PEG dialdehyde or any small molecule dialdehyde or small molecule diepoxide that is a solid), may be admixed with chitosan or a chitosan salt powder and applied to tissue in dry form. In certain embodiments, the multifunctional reactive molecule is a modified chitosan such as those described above, which may be selected, for example, from the aldehyde-modified chitosan (chitosan having pendant aldehyde groups), epoxy-modified chitosan (i.e., chitosan having pendant epoxide groups) and genipin-modified chitosan (i.e., chitosan having pendant genipin groups) described above. Once the admixed powder becomes wet (e.g., due to body fluid and/or application of a fluid), the powder constituents dissolve, allowing the multifunctional reactive molecule to crosslink with amines found on the chitosan or the chitosan salt, and to also react with amines found in tissue.

As another example, a first powder comprising a thiol-modified chitosan such as that described above may be admixed a second powder that comprises a molecule that comprises two or more unsaturated groups and applied to tissue in dry form. Examples of molecules that comprises two or more unsaturated groups include acrylate-terminated hydrophilic polymers. Hydrophilic polymers which may be provided with unsaturated termination include those hydrophilic polymers described above. A particular example of a molecule that comprises two or more unsaturated groups is PEG diacrylate. Applying such a powder to tissue and subsequently mixing with saline in situ will follow a Michael addition reaction scheme. At body temperature and the pH of saline (7.4) the two powders crosslink to form a cohesive patch. In certain embodiments, the first powder or the second powder may include a catalyst, such as a base or a nucleophile).

Various further aspects of the present disclosure are provided in the following enumerated paragraphs:

Aspect A1. A method of treating or preventing bleeding at a tissue site comprising: applying chitosan powder to the tissue site, wherein the chitosan powder comprises a chitosan salt, a crosslinked chitosan, a derivatized chitosan, or a combination thereof.

Aspect A2. The method of aspect A1, wherein the tissue site is in a body lumen.

Aspect A3. The method of aspect A2, wherein the body lumen is the gastrointestinal tract.

Aspect A4. The method of any of aspects A1-A3, wherein the chitosan powder is applied via a catheter.

Aspect A5. The method of any of aspects A1-A4, wherein the powder is fluidized in a gas to form a fluidized powder and blown onto the tissue site.

Aspect A6, The method of aspect A6, wherein the fluidized gas is CO₂.

Aspect A7. The method of any aspects A6-A7, wherein the fluidized powder exits the catheter at a velocity ranging from 15 to 50 m/s.

Aspect B1. A preloaded catheter assembly comprising: a catheter having a lumen extending therethrough, a proximal end, and a distal end having an exit orifice, a reservoir comprising a chitosan powder, wherein the catheter assembly is configured to deliver the chitosan powder from the reservoir, through the lumen, and out the exit orifice.

Aspect B2. The preloaded catheter of aspect B1, wherein the catheter assembly further comprises a pressurized reservoir comprising a pressurized gas for delivering the chitosan powder from the reservoir, through the lumen, and out the exit orifice.

Aspect B3. The preloaded catheter of aspect B2, wherein the pressurized reservoir is positioned upstream of the reservoir and the pressurized gas passes through the chitosan powder, thereby fluidizing the chitosan powder in gas for delivery of through the lumen and out the exit orifice.

Aspect B4. The preloaded catheter of aspect B1, the chitosan powder comprises chitosan, a chitosan salt, crosslinked chitosan, derivatized chitosan, or a combination thereof.

Aspect C1. A powder composition for application to a tissue site, the powder composition comprising first particles comprising chitosan, a chitosan salt or a derivatized chitosan admixed with second particles that comprise a crosslinking agent that covalently or non-covalently interacts with the first particles upon exposure to moisture.

Aspect C2. The composition of aspect C1, wherein the first particles comprise a chitosan salt.

Aspect C3. The composition of aspect C2, wherein the crosslinking agent is a polyanionic crosslinking agent.

Aspect C4. The composition of aspect C1, wherein the first particles comprise chitosan or a chitosan salt and the crosslinking agent is a covalent crosslinking agent.

Aspect C5. The composition of aspect C4, wherein the covalent crosslinking agent is selected from a multifunctional epoxy, a multifunctional aldehyde, and genipin.

Aspect C6. The composition of aspect C4, wherein the covalent crosslinking agent is a derivatized polymer.

Aspect C7. The composition of aspect C6, wherein the derivatized polymer is selected from an aldehyde derivatized polymer, epoxy derivatized polymer, and a genipin derivatized polymer.

Aspect C8. The composition of aspect C6, wherein the derivatized polymer is derivatized chitosan.

Aspect C9. The composition of aspect C8, wherein the derivatized chitosan selected from aldehyde derivatized chitosan, epoxy derivatized chitosan, and genipin derivatized chitosan.

Aspect C10. The composition of aspect C1, wherein the first particles comprise a derivatized chitosan.

Aspect C11. The composition of aspect C10, wherein the second particles comprise a covalent crosslinking agent.

Aspect C12. The composition of aspect C11, wherein the covalent crosslinking agent is a polymeric crosslinking agent.

Aspect C13. The composition of aspect C10, wherein the first particles comprise thiol-modified chitosan and the second particles comprise a molecule having a plurality of unsaturated groups.

Aspect C14. The composition of aspect C13, wherein the molecule having a plurality of unsaturated groups is a hydrophilic polymer having unsaturated end groups.

Aspect D1. A powder composition for application to a tissue site, the powder composition comprising chitosan crosslinked with a multifunctional carboxylated polymer.

Aspect D2. The composition of aspect D1, wherein the carboxylated polymer is a hydrophilic polymer having carboxylic acid end groups.

Aspect D3. The composition of aspect D1 or D2, chitosan is crosslinked with the multifunctional carboxylated polymer using a diimide coupling.

Aspect E1. A powder composition for application to a tissue site, the powder composition comprising derivatized chitosan.

Aspect E2. The powder of aspect E1, wherein the derivatized chitosan reacts with tissue upon exposure to moisture.

Aspect E3. The powder of aspect E1, wherein the derivatized chitosan reacts with primary amine groups in tissue upon exposure to moisture.

Aspect E4. The powder of aspect E2, wherein the derivatized chitosan is chitosan derivatized with a multifunctional aldehyde.

Aspect E5. The powder of aspect E2, wherein the derivatized chitosan is chitosan derivatized with a multifunctional epoxide.

Aspect E6. The powder of aspect E2, wherein the derivatized chitosan is chitosan derivatized with genipin.

Aspect E7. The powder of aspect E1, wherein the derivatized chitosan interacts with thiol groups in tissue upon exposure to moisture.

Aspect E8. The powder of aspect E7, wherein the derivatized chitosan is chitosan derivatized with unsaturated groups.

Aspect E9. The powder of aspect E7, wherein the derivatized chitosan is derivatized with thiol groups.

Aspect E10. The powder of aspect E9, wherein the chitosan is derivatized with a compound comprising a carboxylic acid group and a thiol group.

Aspect E11. The powder of aspect E10, wherein the chitosan is derivatized using diimide (e.g., EDC or DCC) coupling.

EXAMPLE

Chitosan obtained from Sigma Aldrich is suspended in water at a concentration of 2 wt % Chitosan and 98 wt % water. The mixture is stirred using a mechanical mixer at room temperature. Acetic acid is then added during the stirring such that the pH levels out near 5.0 after 5 hours of stirring. 2 wt % citric acid (relative to the weight of chitosan initially used) is added to the container and mixed for an additional 5 hours. This process forms a gel which is subsequently dried. The dried gel is then ground into a fine powder for use. 

1-20. (canceled)
 21. A method of treating a tissue site comprising: administering a composition to the tissue site; wherein the composition includes a powder that comprises first particles comprising chitosan or a chitosan salt and second particles that comprise a crosslinking agent, wherein the crosslinking agent is a derivatized polymer selected from an epoxy derivatized polymer, an acrylate derivatized polymer, or a genipin derivatized polymer.
 22. The method of claim 21, wherein the composition is applied via a catheter.
 23. The method of claim 21, wherein the composition is fluidized in a gas to form a fluidized powder and blown onto the tissue site.
 24. The method of claim 23, wherein the gas is CO₂.
 25. The method of claim 23, wherein the fluidized powder is applied using a catheter and wherein the fluidized powder exits the catheter at a velocity ranging from 15 m/s to 50 m/s.
 26. A composition comprising: first particles comprising chitosan or a chitosan salt; and second particles comprising a crosslinking agent, wherein the crosslinking agent is selected from an epoxy derivatized polymer, an acrylate derivatized polymer, a genipin derivatized polymer, a multifunctional epoxy, acrylate, or genipin.
 27. The composition of claim 26, wherein the crosslinking agent is the epoxy derivatized polymer or the acrylate derivatized polymer.
 28. The composition of claim 26, wherein the first particles comprise a chitosan salt, wherein the chitosan salt comprises a chitosan halide, a chitosan salt of an organic mono-acid, or a chitosan salt of an organic diacid.
 29. The composition of claim 26, wherein the epoxy derivatized polymer is epoxy derivatized chitosan, the acrylate derivatized polymer is acrylate derivatized chitosan, and the genipin derivatized polymer is genipin derivatized chitosan.
 30. A method of treating or preventing bleeding at a tissue site comprising applying the composition of claim 26 to a gastrointestinal tract through an endoscope.
 31. The method of claim 30, wherein the composition is fluidized in a gas to form a fluidized powder composition and blown onto the tissue site.
 32. The method of claim 31, wherein the gas is CO₂.
 33. The method of claim 31, wherein the fluidized powder exits the endoscope at a velocity ranging from 15 m/s to 50 m/s.
 34. A composition comprising: first particles comprising a modified chitosan selected from an aldehyde modified chitosan, epoxy modified chitosan, chitosan modified with unsaturated groups, chitosan derivatized with a multifunctional epoxide, acrylate modified chitosan, or thiol-modified chitosan; and second particles comprising a covalent crosslinking agent; wherein the composition is in the form of a powder; and wherein the covalent crosslinking agent is a molecule having a plurality of unsaturated groups when the first particles comprise thiol-modified chitosan.
 35. The composition of claim 34, wherein the molecule having a plurality of unsaturated groups comprises a hydrophilic polymer having unsaturated end groups.
 36. The composition of claim 35, wherein the molecule having a plurality of unsaturated groups is polyethylene glycol diacrylate.
 37. A method of treating or preventing bleeding at a tissue site comprising applying the composition of claim 34 to a gastrointestinal tract through an endoscope.
 38. The method of claim 37, wherein the composition is fluidized in a gas to form a fluidized powder and blown onto the tissue site.
 39. The method of claim 38, wherein the gas is CO₂.
 40. The method of claim 38, wherein the fluidized powder exits the endoscope at a velocity ranging from 15 m/s to 50 m/s. 